Metering lever

[weenieroaster]

I haven't seen this addressed anywhere:

When the metering lever is pushed down by the diaphragm, it is supposed to raise the inlet needle accordingly. Sometimes, there is a bit of play in the needle slot, so that the lever moves up before the hook end contacts the upper edge of the needle slot and begins raising the needle. On some rebuild kits, the lever is thinner material than on the stock one, which increases the amount of upward travel before the needle starts to actually raise up. I found that you can't adjust the hook end to always be in contact with the needle to raise it without the delay, the spring pushes the end down, and if you try to bend up the hook too much, the needle binds.

The question is, if there is this play or delay in raising, should it be taken into consideration when adjusting the lever in relation to the metering floor or carb body, whatever the specs call for. I'm thinking that raising up the lever higher than recommended, the amount of discrepancy between the arm thickness and needle slot, will then give the right amount of needle movement. Perhaps it's not critical? Any thoughts?

 

[Edge & Engine]

Well, when you set the lever to the proper level, it shouldn't make any difference what the thickness is, right? I'm thinking that when you set it, if the lever is thinner, you will have to bend it more to attain the correct height. But I kind of doubt that it's that critical.

 

[weenieroaster]

I don't know if it's even worth bothering about.....but bending the lever doesn't make any difference in terms of where the fork end contacts the slot. The spring pushes the lever up at the diaphragm contact point, so the fork end at the needle will always sit contacting the lower edge of the needle slot. It's the gap above that causes the delay in raising the needle. With a thin metering arm, it can be fairly large.

 

[Edge & Engine]

I don't know if it's even worth bothering about.....but bending the lever doesn't make any difference in terms of where the fork end contacts the slot. The spring pushes the lever up at the diaphragm contact point, so the fork end at the needle will always sit contacting the lower edge of the needle slot. It's the gap above that causes the delay in raising the needle. With a thin metering arm, it can be fairly large.

But why wouldn't you just set the lever like the mfg recommends?

 

[weenieroaster]

Well, I was comparing four carbs, and two had virtually no play, so that when the lever was pushed down, the needle instantly raised up. On the other two, there was a gap above the fork at the slot, so there was a delay before the needle started to raise. One had a recently installed carb kit, and the lever looked very cheapo thin, even though a Stihl rebuild kit. The lever had to be pushed down like one fourth of it's travel, before the needle started to raise. I tried to adjust that out, bending up the fork at the needle end, but to get it where the needle instantly moves up, the needle will bind from the curve of the fork pulling it inward.....something along those lines. I'm wondering if this could be a factor in low to mid range rpm, because the needle isn't clearing the orifice sufficiently, or perhaps a hesitancy in spool-up?

 

[Lakeside53]

Contrary to widely held beliefs... above a few thousand rpm, the metering needle does not move for every intake stroke, but settles at some mid-point proportional to the fuel flow needs...

And as for the arm thickness... not important.

 

[pioneerguy600]

Well, I was comparing four carbs, and two had virtually no play, so that when the lever was pushed down, the needle instantly raised up. On the other two, there was a gap above the fork at the slot, so there was a delay before the needle started to raise. One had a recently installed carb kit, and the lever looked very cheapo thin, even though a Stihl rebuild kit. The lever had to be pushed down like one fourth of it's travel, before the needle started to raise. I tried to adjust that out, bending up the fork at the needle end, but to get it where the needle instantly moves up, the needle will bind from the curve of the fork pulling it inward.....something along those lines. I'm wondering if this could be a factor in low to mid range rpm, because the needle isn't clearing the orifice sufficiently, or perhaps a hesitancy in spool-up?

Don`t bend the fork end, just set the diaphram contact end to factory spec and the other things you mentioned will not affect the operation of the carb . I have done hundreds of carb rebuilds and will reuse the OEM metering levers if at all possible ,never found a broken one and very few worn out ones,usually the OEM ones are of better quality than some of the aftermarket carb kits out there.IMO. Pioneerguy600

 

[weenieroaster]

OK guys, I'm going to consider the case closed and not worth thinking about I'll set to factory specs.

Thanks for the help!